| Definition -
A language — such as English — in which almost all sentences must have a subject, even if there is nothing for the subject to refer to, e.g. the use of pleonastic subjects in sentences such as It is raining.
As opposed to a topic-prominent language, which is a language — such as Japanese — that organizes its syntax into a topic–comment structure. For example, in Japanese Sono yashi-wa happa-ga ookii translates to "That palm tree [topic] leaves are big [comment]."
1. Nothing is cut and dried: Even English sometimes uses topic-prominent sentences, e.g. John, I never really liked him.
Etymology - According to the Wikipedia, the term was popularized in American linguistics by Charles Li and Sandra Thompson.